Typically, methods of forming TCOs on glass substrates require high glass substrate temperatures. Such methods include chemical pyrolysis where precursors are sprayed onto the glass substrate at approximately 400 to 500 degrees C., and vacuum deposition where the glass substrate is kept at about 150 to 300 degrees C. Sputter deposition of a TCO at approximately room temperature would also be desirable, given that most float glass manufacturing platforms are not equipped with in-situ heating systems.
There is often a need to thermally temper coated articles having a glass substrate coated with a TCO film/coating. For instance, in certain applications tempering is required by code (e.g., e.g., for windows over doorways, for windows identified as breakable windows for firemen, and other applications). Thermal tempering typically requires heating the glass substrate with a coating thereon in a tempering furnace at a temperature of at least about 580 degrees C., more preferably at least about 600 degrees C., and often at least about 620 or 640 degrees C. (e.g., for at least about 2 minutes, more preferably for at least about 5 minutes). Thus, it will be appreciated that thermal tempering involves very high temperatures.
Conventional temperable TCOs use pyrolytically processed fluorine-doped tin dioxide as the material for the TCO coating. However, it would also be desirable for a TCO to be able to be deposited by sputtering so that it could be performed at approximately room temperature.
However, glass supporting sputter-deposited TCOs cannot be thermally tempered without the TCOs suffering a significant loss in electrical conductivity. Glass tempering temperatures (see above) cause a rapid conductivity drop in certain TCOs (e.g., sputter-deposited zinc oxide inclusive TCOs). It is believed that this drop in conductivity is due to oxidation of the TCO during the tempering process.
Thus, it will be appreciated that there exists a need in the art for an improved technique or method of tempering glass substrates including TCO films/coatings thereon, which can prevent or reduce oxidation of the TCO during tempering and thus allow the TCO to substantially maintain its electrical conductivity in certain example instances.
In certain example embodiments of this invention, a method is provided for thermally tempering a glass substrate with a TCO film/coating thereon. The thermal tempering typically involves heating the glass substrate with the TCO coating thereon in a tempering furnace at a temperature of at least about 580 degrees C., more preferably at least about 600 degrees C., and often at least about 620 or 640 degrees C. The glass substrate with the TCO coating thereon may be in the tempering furnace for at least about 2 minutes, more preferably for at least about 5 minutes, in certain example embodiments of this invention. In certain example embodiments, flame(s) are provided proximate the exposed surface of the TCO in the tempering furnace in order to burn off excess oxygen near the TCO surface thereby preventing or reducing oxidation of the TCO during the tempering process. By reducing oxidation of the TCO during the tempering process, more of the electrical conductivity of the TCO coating can be maintained during and/or after tempering.
In certain example embodiments, the flame(s) need not be provided in the entire tempering furnace. In certain example embodiments, the flame(s) are provided in locations so that the flame are only proximate the surface of the TCO film once the glass and/or TCO film reaches a predetermined temperature at or near the TCO oxidation temperature which can vary based on the material making up the TCO film.
In certain example embodiments of this invention, the TCO film may be sputter-deposited on a glass substrate (either directly or indirectly) at approximately room temperature. In alternative embodiments, it is possible to pre-heat the glass substrate prior to the sputter-deposition of the TCO film. In certain example embodiments, however, the flame(s) discussed herein may be used in connection with tempering TCO films deposited via pyrolysis. Example TCO films include films of or including ZnAlOx:Ag, ZnO, ITO (indium tin oxide), SnO2 and/or SnO2:F. Other types of TCO films may instead be used.
In certain example embodiments of this invention, there is provided a method of making a coated article including a transparent conductive film, the method comprising: providing a glass substrate; forming a film comprising a transparent conductive oxide on the glass substrate; and tempering the coated article including the glass substrate and the film comprising the transparent conductive oxide, and wherein at least one flame is provided in a tempering furnace in order to burn off oxygen to prevent or reduce oxidizing of the film comprising transparent conductive oxide during tempering.
In other example embodiments of this invention, there is provided a method of making a coated article including a transparent conductive film, the method comprising: providing a glass substrate; forming a transparent conductive film comprising a transparent conductive oxide on the glass substrate; and tempering the coated article including the glass substrate and the transparent conductive film, and wherein at least one flame is provided in a tempering furnace proximate the transparent conductive film.